A lithium battery is characterized by having high voltage and energy density and less memory effect, and thus, is used for various intended purposes such as power sources of vehicles, mobile devices and the like, and storage batteries in facilities, houses and the like. Accordingly, the study of a lithium battery has been actively conducted. As the use thereof advances, a further improvement in safety and performance has been desired for a lithium battery.
In order to improve safety, an abnormality, such as an overcharge, has to be prevented from occurring in a lithium battery. In a battery using a flammable organic electrolytic solution as an electrolyte, a decomposition additive which decomposes at a predetermined voltage or more to produce gas is added to the electrolytic solution and a pressure-type current interruption mechanism is embedded. By using the pressure-type current interruption mechanism, when the decomposition additive decomposes to produce gas and the pressure increases in the battery, the current interruption mechanism deforms to interrupt a charge current. Accordingly, an overcharge is suppressed and a temperature increase or the like of the battery is prevented from occurring.
On the other hand, as a method for the improvement in the safety and performance, an all-solid-state battery using a solid electrolyte has been studied. An all-solid-state battery is regarded as having higher safety compared with a liquid battery since a flammable organic electrolytic solution is not used, but in order to secure higher safety, it is very important to detect an overcharge with high accuracy and to deal with it. However, since a solvent is not used in an all-solid-state battery, a decomposition additive used in an organic electrolytic solution cannot be used. Even if there is an appropriate decomposition additive which can be used in a solid electrolyte, the number of parts which do not normally contribute to power generation, such as a decomposition additive and a current interruption mechanism, may be increased.
In connection with prevention of an overcharge of an all-solid-state battery, for example, Patent Literature 1 discloses a solid-state battery module. The solid-state battery module is formed by laminating a plurality of solid-state batteries each of which includes a power generation unit and an overcharge prevention unit between a pair of current collectors. The power generation unit includes, for example, a positive electrode layer, a negative electrode layer and a solid electrolyte layer interposed therebetween. The overcharge prevention unit is made from a polymer material whose electric conductivity is increased at a predetermined voltage or more. The purpose of Patent Literature 1 is to easily control an overcharge and to appropriately prevent each single battery from being in an overcharge state.